1. Field of Invention
The present invention relates to a method of controlling light and to an apparatus for controlling light using a photo-responsive element useful in the field of photoelectronics and photonics, such as optical communication and optical information processing.
2. Description of Related Art
For the purpose of ultra-high speed transduction and processing of information, in the field of optical electronics and photonics focused on the multiplicity and high density of light research and development on the light-light controlling method (method of controlling light by light) have been ardently made aiming at the modulation of the intensity (amplitude) or frequency (wavelength) of light utilizing the changes in the transmittance and refractive index caused by illuminating the optical element formed by processing optical materials or optical compositions without depending on electronic circuit techniques. In addition, when the parallel optical logical operation and imaging are intended to make the best use of the characteristics of light, a "spatial light modulator" for performing a certain modulation such as a modulation of the photointensity distribution on the beam-section (bundle of rays) is extremely important, wherein the application of said light-light controlling method is also highly expected.
As the phenomena wherein the application for the light-light controlling method is expected, the nonlinear optical effect such as the saturable absorption, nonlinear refraction and photoreactive effect, and photochromic phenomenon is of great interest.
On the other hand, the phenomenon wherein a molecule excited by the light in the first wavelength band region newly absorbs the light in the second wavelength band region different from the first wavelength band region has been known, and this phenomenon may be called "excited state absorption" or "induced absorption", or "transient absorption".
As an example of attempting to apply excited state absorption, Japanese Patent Laid-open Publication No. Sho 53-137884, for example, discloses an optical modulation method wherein a solution or solid containing compounds of the porphyrin series and an electron receptor was illuminated with lights of two different wavelengths, resulting in the transduction of the information of the one light of the one wavelength to the wavelength of the other light. Also, Japanese Patent Laid-open Publication No. Sho 55-100503 and Japanese Patent Laid-open Publication No. Sho 55-108603 disclose an optical fiber of the functional liquid core-type which selects the propagation light corresponding to the time-dependent variation of the excited light utilizing the spectrum difference between the ground and excited states of porphyrin derivatives. In addition, Japanese Patent Laid-open Publication No. Sho 63-89805 discloses an plastic optical fiber containing organic compounds such as porphyrin derivatives in its core which show the absorption corresponding to the transition to the more higher triplet state from the light-excited triplet state. Also, Japanese Patent Laid-open Publication No. Sho 63-236013 discloses an optical functional element wherein, after the crystalline cyanine dye such as cryptocyanine is illuminated with a light of the first wavelength to excite the molecule, said molecule is illuminated with another light of the second wavelength different from the first wavelength, thereby the transmittance or reflection of the light of the second wavelength is switched by the light-excited state by the light of the first wavelength. Furthermore, Japanese Patent Laid-open Publication No. Sho 64-73326 discloses an optical signal modulating medium which optically modulates utilizing the absorption spectral difference between the excited and ground states induced by illuminating the optical modulation medium comprising a light-induced electron migration material such as porphyrin derivatives dispersed in the matrix materials with the lights of the first and second wavelengths.
As the construction of the optical apparatus used in the conventional techniques, Japanese Patents Laid-open Publications No. Sho 55-100503, No. Sho 55-108603, and No. Sho 63-89805 disclose an apparatus construction wherein the light source of exciting light (e.g., flush lamp) is wound by the optical fiber propagating the propagation light. Japanese Patent Laid-open Publications No. Sho 53-137884 and No. Sho 64-73326 disclose the apparatus construction wherein the whole portion within the photo-responsive optical element where the light corresponding to the signal light propagates is illuminated with the light corresponding to the control light from the different direction from that of the light path of the signal light without said control light being converged, but rather diverged by means of a projecting lens, etc.
However, because of the requirement for the light power of extremely high density to give rise to changes in the transmittance or refractive index (photoresponse) large enough for practical use, the slow response to light illumination, and the low durability of photoresponsive materials in the conventional techniques, an apparatus for controlling light for practical usage has yet to be obtained.
It is the object of the present invention to solve the above-described problems and provide a method and apparatus of controlling light to obtain the sufficiently large photoresponse with a superior reproducibility.